I could say that software hasn't changed much since the 50s as we still process in binary. Shouldn't we have moved to quantum computing by now already with multiple superposition states?
Well, no, software has changed considerably both because the underlying technology has improved and because the discipline of software development has become more sophisticated. The problems people are willing to pay to solve have also changed. I've been in the industry since 1983 and it was an absolute whirlwind until 1998 and has slowed down since then. But there's still more innovation than in SCUBA. The technology keeps improving, and that opens up new application areas where there previously just wasn't enough computing or storage capacity available at reasonable cost to make them workable. We had video editing in the lab back in the 1980s but the render times were awful even with the low resolutions of the day, and now I can edit 1080p at home, which means there's software to be written for video editing and sharing and so on.
During the same span of time recreational scuba has only changed around the margins because the technologies that make it go were good enough in 1980. SCUBA relies on two critical technologies. One of them is elastomers, because without effective exposure suits, hoses, masks, and other rubber goods, diving is primitive and unsafe. The other one is compressed gas technology, particularly the ability to produce high pressure cylinders that are safe and then fill them with breathable gas. The regulators are child's play to manufacture compared to what goes into making a compressor, a filter tower, and a cylinder.
scuba gear has a different set of challenges than terrestrial equipment, namely it has to take into account being watertight, pressure resistant, corrosion resistant, and account for buoyancy rather than just dry weight. Combined with the small market and you have limited options for improvement along with lengthy payback periods for product lines.
a jetfin is still popular because of its weight, rigidity, and ruggedness. you may be able to make a carbon fiber fin that is really lightweight, but it will be too light for use with a drysuit and may be fragile so that it breaks in two years. so why should a diver pay for something that is unsuitable for their use and would not last as long.
You're guessing at what the industry is like but that's understandable since you're new. There are carbon fiber fins, see
PURE Carbon Fiber Freedive Fins | MAKO Spearguns, and they make sense for freediving but generally not for scuba. They last a long time as long as you don't do giant strides with them.
I don't think jetfins are as popular as you seem to think they are.
The innovation in SCUBA equipment in recent years has mainly been in rebreathers. Those don't appeal to me much right now because they are not useful for the kinds of dives I make. Maybe someday.
